1. Field of the Invention
The present invention relates to an image forming apparatus having a function whereby a sheet of paper on which an image has been formed, at an image forming section, is again supplied thereto in order for images to be formed on both sides of the paper sheet, or for overlapping images to be formed on one side thereof.
2. Description of the Related Art
An electronic copying machine having the above-described function has been developed in recent times, and includes a copying unit for forming copied images on a paper sheet, and a supply unit for resupplying the same paper sheet to the copying unit, in order for another image to be formed thereon. The above electronic copying machine operates as follows:
First, with the copying machine being in the overlap copying mode, a single sheet of paper from a paper-storage cassette attached to the copying unit is picked up by means of paper supply rollers, is aligned by a pair of first aligning rollers, and then fed between a photosensitive drum and a transfer charger, the transfer charger causing a toner image to be transferred from the photosensitive drum to one side of the paper sheet. After the toner image has been fixed to the paper sheet by a pair of fixing rollers, the sheet is introduced, through a first gate, to a stacker of the re-supply unit. Paper sheets stacked in the stacker are picked up one by one by pickup rollers, are aligned by a pair of second aligning rollers, and then fed, through a second gate, to the first aligning rollers at the copying unit, and again between the photosensitive drum and transfer charger, where another toner image is transferred from the photosensitive drum onto that side of the paper sheet on which the preceding image was formed. Thereafter, the paper sheet is discharged onto a discharge tray, via the fixing rollers and a pair of discharge rollers.
With the copying machine in the double-sided copying mode, paper sheets stacked in the stacker are, as in the case of the overlap copying mode, picked up one by one by the pickup rollers, are aligned by the second aligning rollers, and then fed, through the second gate, to a pair of switchback rollers which change the sheet-conveying direction. A paper sheet whose conveying direction has been thus changed is then fed, through a third gate, to the first aligning rollers at the copying unit, where a toner image is transferred from the photosensitive drum onto that side of the paper sheet which is opposite to the side on which an image was formed in the preceding image-forming step. Thereafter, the paper sheet is discharged onto the discharge tray, via the fixing and discharge rollers.
The stacker, the pickup rollers, the aligning rollers, the second gate, the third gate, and the switchback rollers are assembled as a single pull-out unit which can be readily removed from the resupply unit.
Thus, when a sheet of paper becomes jammed between the aligning rollers at the copying unit and the aligning rollers at the resupply unit, or between the aligning rollers at the copying unit and the switchback rollers at the resupply unit, the pull-out unit is removed from the resupply unit, whereby the jammed paper sheet can be more easily removed.
However, when a paper sheet is jammed such that its back end is held between the second aligning rollers or switchback rollers, with its front end introduced into the copying unit, then the sheet will be torn in two upon removal of the pull-out unit, thereby making it more difficult to eliminate the jamming.